Fig. 2

Diagrams for a = 3.8 mm. a Band diagram below light lines with frequency in GHz. The inset shows the Brillouin zone and high-symmetrical points. b–d IFCs of the first three bands in the first Brillouin, respectively, where the gray discs located at the center are the light cones at 3 GHz, 9 GHz, and 12.5 GHz, respectively, the frequency values are marked in GHz, and the frequency increases from blue to orange. e Transmission spectra at normal incidence obtained from simulations (EMT) when the electric field is polarized along the x- and y-directions, corresponding to the black line (point) and the red line (point), respectively. Insets are the E_z distribution at different resonances with values varying from –max (blue) to max (red). f Relative permittivity obtained from EMT, where the gray regions indicate the frequency ranges of hyperbolic IFCs predicted by EMT